In railway signalling technology, the interruption of electric power to a load is of the greatest importance, the load being e.g. a signal lamp which, when illuminated, announces "permission to pass" for a train. Relays have so far been used in the art to achieve this interruption. However, relays are burdened with the disadvantages that they are of large size as well as heavy, expensive to manufacture, and environmentally sensitive and in that they have limited working life with respect to the number of interruptions which can be expected.